Artificial Tooth Structure

Abstract

An artificial tooth comprising a crown section; a root section adapted to be inserted into an alveolus in the jaw of a vertebrate, the root section being formed by a member of a carbon material which is microcrystalline in structure and substantially impermeable and having at least one substantially cone-shaped projection adapted to fit approximately within the inner surface of the alveolus; and means resiliently securing the crown section to the root section. The resilient securing means are arranged such that they are capable of absorbing sudden shocks which might be applied to the artificial tooth structure such as by biting upon something unexpectedly hard.

Description

This invention relates to an artificial tooth structure based on an implant to take the place of the root of an extracted tooth.

Dental implants for insertion into an alveolus in the jaw of a vertebrate to form the root section of an artificial tooth are described in our co-pending patent application Ser. No. 200,313.

A natural tooth is supported in the alveolus of the jaw bone by a periodontal ligament which includes fibrous connecting tissue extending between the cementum of the tooth root and the jaw bone itself, which fibres are normally in tension.

The natural tooth is thus resiliently supported for a very limited amount of movement in both horizontal and vertical directions and is thus capable of absorbing sudden shocks which might be applied to it such as by biting upon something unexpectedly hard.

With an artificial tooth structure which is based upon an implant, it is known that a regular periodontal ligament forms about the implant and tends to retain the implant in position within the alveolus. It is, however, thought that the jaw bone growth which occurs after implantation is a major contributory factor in implant retention, therefore, the root section of an artificial tooth is more rigidly attached to the jaw bone than the root section of a natural tooth. The previously mentioned unexpected shocks which a relatively rigid retained artificial tooth could be subjected to might, especially with an implant of vitreous carbon, which is itself a relatively brittle material, give rise to substantial damage.

Carbon materials which are microcrystalline in structure and substantially impermeable, for example those known as vitreous, glassy and pyrolytic carbons are chemically, biologically and physically compatible with animal tissue and are, therefore, ideally suited for use in the fabrication of artificial tooth structures.

This invention provides an artificial tooth comprising a crown section; a root section adapted to be inserted into an alveolus in the jaw of a vertebrate, the root section being formed by a member of a carbon material which is microcrystalline in structure and substantially impermeable and having at least one substantially cone-shaped projection adapted to fit approximately within the inner surface of the alveolus; and means resiliently securing the crown section to the root section.

In one form the root section, which is of a carbon material such as vitreous carbon that is microcrystalline in structure and substantially impermeable, is provided with means for facilitating the securing of the root section within the alveolus, and is provided with one or more integral or attachable stub extensions, the crown section being fastened to the or each stub extension by an intermediate elastomeric material. The elastomer may be rubber and may be preformed, and the stub extensions may have bulbous heads so that as the crown is forced into position over such a head or heads the elastomer is squeezed into a state of compression so as to support the crown section of the artificial tooth in a flexible manner, preferably comparable to the flexibility provided by the natural periodontal ligament. In this case the amount and shape of the elastomeric material may be so chosen and controlled by moulding that sufficient of the elastomer is extruded by the squeezing-on process to form a reasonable seal between the edge of the crown section and the root section.

As an alternative arrangement the elastomer may be, for example, a fast curling silicone rubber which is injected under pressure into the space between the or each stub extension and the crown section, the latter being supported by a jig type of device while curing takes place.

The securing of the root section within the alveolus can be effected by any one of the methods outlined in our co-pending patent application Ser. No. 200,313.

The drawings show rather schematically a section in FIG. 1 of a human tooth, this consists of a crown 1 of enamel supported by a main body of dentine 2, which in the root portion is surrounded by a layer of cementum 3. This root portion is supported in the alveolar socket of the jaw bone 4 by fibrous material forming part of the periodontal ligament and shown schematically by the fibres 5.

FIG. 2 shows a similar socket in which an implant 6 of for example vitreous carbon, has been inserted, after extraction of the natural tooth to form the root section of an artificial tooth.

This implant has grooves 7 running around its outer surface and alveolar bundle bone 8 has grown into contact with the implant 6 so as to hold it rigidly in the jaw bone.

The implant 6 has an integral stub extension 9 which has closely controlled dimensions and which is non-circular. The head of the stub projects only slightly beyond its neck and an artificial crown section 10 of, for example, a plastics material, is provided with a complementary cavity to fit over the stub with an intermediate member 11 of an elastomeric material such as rubber. The volume of the member 11 is chosen so that when the crown section 10 is forced into position over the head of the stub 9 the elastomeric material of the member 11 is caused to flow in a direction towards the exterior of the artificial tooth. The lower edges of the cavity in the crown section 10 are relieved as shown at 12 to accommodate the elastomeric material of the member 11, which is caused to flow outwards.

The elastomeric material which is trapped between the crown section and the stub 9 is thus caused to be in compression as is the remainder of the member 11 which lies between the upper shoulders 13 of the implant 6 and the lower surfaces of the crown section 10.

Thus, although the root section 6 of the artificial tooth is rigidly held in the alveolus by the jaw bone growth, the crown itself is, due to the resilient mounting provided by the member 11, capable of limited flexibility in relation to the root section so that the natural condition of a tooth is simulated and it is enabled to accommodate itself to certain shock loads.

In order that the crown section may be successfully forced onto the stub 9 without exerting too much pressure on the alveolar bone, the crown section 10 may be provided with at least two lateral passages such as the passage 14 in which levers may be inserted so as to contact the lower side of the head of the stub 9 and enable the crown section to be forced down into position against the forces exerted by the member 11. After the crown section is in position the passages 14 may be plugged with suitable material.

A further form of the invention is shown in FIG. 3, in which the alveolus from which a natural tooth has been extracted, has had inserted into it an implant 21. The gingival tissue 31 would have been sutured over the implant 21 to hold it in position in a preliminary healing period during which bundle bone 22 will have grown inwards from the alveolar cavity into contact with the implant 21 so as to enter its peripheral grooves and hold it firmly in position in the alveolus.

The upper surface of the implant 21 is formed with a recess 23. Preferably with roughened or grooved walls, and receives a peg portion of a bulbous spigot 24. The peg portion of the spigot 24 is secured in the recess of the implant 21 by a suitable cement 32. The spigot 24 therefore provides a stub extension in the implant 21.

When the cement 32 is adequately set an artificial crown section 26 for example of acrylic resin, is placed over the bulbous portion of the spigot 24, and is held in place by a somewhat flexible and preformed basket-like member 27 which is previously inserted into a cavity in the crown section 26 and which is shaped to conform to the interface between the crown section 26 and the root section 21 and arranged to provide a space around the spigot 24 within the cavity of the crown section 26. When the crown section 26 is thus held in position a fast curing elastomeric material 28 such as for example Dow Corning sealant is injected into this space through an aperture 29 in the wall of the crown section 26 so as to fill the space between the wall of the cavity of the crown section 26 and the spigot 24 and so as to slightly exude therefrom around the approximately annular gap between the lower edge of the crown section 26 and the upper surface of the implant 21.

The gingival tissue 31 is shown for clarity spaced apart from the implant 21 but after a further period of healing it will grow inwards and the level of the joint between the crown section 26 and the implant 21 is prefereably arranged such that after healing the gingival tissue 31 will cover it.

The material and structure of the member 27 is such that it provides sufficient friction to hold the crown section 26 in position during the curing of the elastomeric material 28. The member 27 may, for example, be moulded from polyvinylchloride, the hardness of which may be suitably controlled by choosing the proportion of plasticiser that it contains.

The dimensions of the bulbous spigot 24 which forms the stub extension are accurately controlled as are those of the cavity within the crown section 26 so as to define between them a space which when fitted with the chosen elastomeric material 28 will permit a degree of resilient movement of the crown section when in use such as to cushion the implant 21 from damaging shock and the bone of the jaw from unpleasant jarring.

The method outlined in preceding paragraphs in relation to FIG. 3 can be used for the root structure of FIG. 2 in order to secure the crown section 10 to the integral stub extension 9 of the root section 6.

This method of resiliently securing the root section to a crown section has the advantage that fewer crown shapes and sizes need to be stocked since the attitude and projection of the crown section can, to some extent, be self-adjusting by contact with teeth in the opposite jaw while curing of the elastomeric material is taking place.

It is to be understood that the foregoing description of specific examples of this invention is made by way of example only and is not to be considered as a limitation in its scope.

Claims

What is claimed is:

1. An artificial tooth comprising a crown section; a root section adapted to be inserted into an alveolus in the jaw of a vertebrate, the root section being formed by a member of a carbon material which is microcrystalline in structure and substantially impermeable and having at least one substantially cone-shaped projection adapted to fit approximately within the inner surface of the alveolus; and means resiliently securing the crown section to the root section, the resilient securing means including at least one stub extension for the said member, the stub extension fitting into a complementary cavity in the crown section; and an elastomeric material interposed between the stub extension and the wall of the cavity and between the lower surface of the crown section and those regions of the upper surface of the said member which surround the stub extension, the elastomeric material being preformed and shaped to conform to the profile of the interface between the crown section and the root section, each stub extension having a bulbous head causing the preformed elastomeric material to be in a state of compression and such that it effects a substantial seal between the edge of the crown section and the root section.